PolymerTEnTAFRågoR Flashcards
An extruded isotactic polypropylene homopolymer (Tg = -10 ºC; Tm = 165 ºC)
is completely transparent. What could be the cause? Could you recycle such a material?
Rapid cooling prevented crystallisation; yes, polypropylene is a thermoplastic polymer
What is one similarity and one difference in structure between a thermoset and an
elastomer?
Similarity: they are both amorphous and crosslinked polymers; difference: crosslink density.
State the accepted abbreviation and the minimum repetitive structural component of
polyvinyl chloride
Polyvinyl chloride - PVC. The repeating unit is C2H3CL
Name the processing and, if is the case, the secondary shaping method for producing the plastic
parts in the figure below:
(1) Kevlar (Poly-paraphenylene terephthalamide) fibers for bullet-proof vests
(2) acrylonitrile butadiene styrene (ABS) shelf profiles
(3) ABS Lego sword
(4) ABS car rear spoilers
1) extrusion + fiber spinning; (2) extrusion; (3) injection molding; (4) injection molding.
what is the role of the metering region of a single-screw extruder screw?
build up pressure.
what are the main four units of an injection molding machine (
Injection unit, plasticating unit, mold and ejection unit.
What does it mean that the viscosity function of a polymer melt is shear thinning?
Viscosity decreases with increasing shear rate
Sketch the typical stress-strain diagram of an amorphous polymer at room temperature in a
short term tensile test. What causes the loss of linearity in the curve?
crazing (microcracks)
Consider the structure of vinyl polymers: C2H3X
Give two examples of the side group X, specifying the chemical formula and the name of the polymer
How is the polydispersity index (dispersity) defined and explain its significance
E.g. X= H Polyethylene (PE), X = CH3 Polypropylene (PP), X = C6H5 Polystyrene (PS), X = Cl
Polyvinylchloride (PVC)
PDI (Ð) = Mw / Mn ,where Mw is the weight-averaged molecular weight and Mn is the number-
averaged molecular weight. (1p) PDI is a measure of how broad the molecular weight distribution
is.
Sketch a typical viscosity function of a molten polymer. What molecular processes make the
viscosity function nonlinear?
The infinite-shear viscosity plateau can also be left out on grounds that it is difficult to reach in
polymer melts. Viscosity function (1p), correct labeling, incl. log-log (1p)
Name the processing and secondary shaping method for producing a yarn of (continuous long)
carbon fibers.
extrusion (1p) with fiber spinning as secondary shaping (1p)
Estimate the length of a fully extended polyethylene molecule knowing that:
Repeting Unit: C2H6
- the molecular weight of the entire molecule is M = 100000
- the molecular weight of the repeating unit is M = 28
- the distance between repeating units is 0.252 nm
n [number of repeating units] = 100000 / 28 = 3571; Estimated length = 3571 x 0.252 = 900 nm
Name four types of polymer additives that are commonly mixed into polymers to improve their
properties (
Examples: fillers, flame retardants, stabilizers against thermal degradation, plasticizers,
antistatic agents, blowing agents, etc
How can thin polymer fibers with highly oriented molecular structure be obtained?
Extrusion + fiber spinning as secondary shaping
In what conditions could an amorphous polymer not exhibit crazing before fracture in a tensile
test?
At high loading rates and/or temperatures around and above Tg
How does pressure affect the melting temperature of a semicrystalline polymer? Illustrate the
effect using a p-V-T diagram
The melting temperature increases with increasing pressure
Define the average molecular weight of a polymeric material (1p). What does the molecular weight
quantify?
The molecular weight quantifies the length of polymer chains (1p). The average molecular weight
is defined as M = W / N
W = weight
N = number of atoms
The strength of a material is determined by the forces holding it together. What are these forces
in polymer components and which one is considered to be dominant in determining their strength
There are two main forces that hold a polymeric material together: (i) covalent bonds that hold
together the C-C backbone (1p) and (ii) intermolecular Van-der-Waals forces (1p). The latter, (ii),
dominate the strength of plastics
When a polymer is pumped through a die, the size of the polymer extrudate is greater than the
size of the die orifice, see Figure 1, phenomenon also known as ‘die swelling’. Briefly explain why
does ‘die swelling’ occur using a sketch or a short description.
After being stretched and oriented through the die, polymer molecules relax to a preferred state
when at atmospheric pressure, resulting in extrudate diameters greater than the die
Name two secondary shaping operations for extrusion, and choose one secondary operation and briefly explain how the process works (sketch included)
Any two of: fiber spinning, film casting and film blowing (1p).
fiber spinning
A polymer melt is pumped through a circular die called a spinneret. Spinneret can
have up to 10 000 holes. The extrudates are drawn at a speed higher than the die
exit speed, resulting in thin filaments.
film casting
A polymer melt is extruded through a slit die unto a chill roll for
cooling wherefrom the film is being transported for storage.
Film blowing
A polymer met is extruded through an annular die and it is drawn and
inflated using an air supply blowing through the center of the annular
die.
Name and write the chemical structure of a plastic material having at least 3 carbons and 5
hydrogen atoms in its repeating unit
polypropylene, polystyrene
Is tacticity and long chain branching the same? Briefly explain
No. Tacticity refers to the positioning of side groups along the carbon backbone while long chain
branching refers to the presence of side chains
What is the difference between a fossil-based polyethylene (PE) and a bio- PE manufactured
from sugar cane
- from chemical structure point of view (1p)
- from a sustainability point of view (advantage and disadvantage).
They are identical from chemical structure point of view. Bio-PE is manufactured from a
renewable resource but is not biodegradable
En termoplast skall väljas till en produkt. Materialet behöver ha måttlig styvhet, god slagseghet i
temperaturområdet –20 till +40 C, god infärgbarhet, låg materialkostnad och vara välkänt vid
användning i rationella tillverkningsprocesser
Föreslå en lämplig typ av plast! Svara genom att ange fullständig benämning, vedertagen
förkortning och repeterande enhet
Vilken styvhet kan uppskattas för ditt föreslagna material enligt a), exempelvis vid korta
belastnings tider?
En lämplig typ av plast är polyeten, HDPE, CH2-CH2
tyvheten för HDPE är ca 1 GPa (0,7 – 1,5)
